Packaging of electronic devices provides mechanical support, protection of the electronic circuitry components, and a medium for interconnecting the chip to a circuit board for use in a system. As systems become smaller, a need exists to make packages as small as possible.
The packaging process begins with the fabrication of a crystalline semiconductor material, usually silicon or gallium arsenide. Individual dies (i.e., chips) are formed on the wafer at the same time. Then the wafer is separate into single dies. One limit in making small packages is the size of the dies (e.g., the size of the silicon).
Each of the individual dies is typically packaged in a chip carrier. External connections on the chip carrier package allow for the chip to be mounted on a printed wiring board. The chip carrier is electrically connected to the printed wiring board by wire bonding leads on the chip carrier through a common mounting surface on the board or by surface mounting the chip carrier directly to the mounting surface.
One method of surface mounting is called controlled collapse chip connection (C4), or commonly referred to as flip-chip or solder bump. A flip-chip is a leadless, monolithic structure that contains circuit elements, which is designed to electrically and mechanically connect to the hybrid circuit means of an appropriate number of bumps that are located on its face and are covered with a conductive bonding agent. In other words, flip-chip is the bonding of chips face down by soldering bonding pads. Thus, flip-chip mounting is a method of mounting a silicon die or substrate without the need for subsequent wire bonding.
Initially in the flip-chip mounting process, a solder ball is formed on the top of each bonding pad. It should be noted that the bonding pads may be placed at any location on the surface of the die. A bonding-pad cap is formed over the solder balls. The die is then heated which causes the solder to recede from the surface and form a solder ball on top of the bonding-pad cap. After testing and separation of the die, each die is placed face down on a laminate substrate. The temperature is increased, which causes the solder to reflow. By reflowing the solder, the die can be bonded directly to the interconnections of the substrate. Thus, the solder balls provide both electrical connection and die attachment. It should be noted that large numbers of bonds may be formed in this manner simultaneously.
In the mounting process, after the solder bumps have been placed on the die, the wafer containing the die is cut to form the individual dies. Some electrical testing is then performed on the chip. The chip is then placed in the system. A heatsink or other apparatus is then attached to the chip to dissipate heat during its operation. The size of the package is limited by its capacity to dissipate heat out from the die.
If after placement in the system, the die is not fully functional, then it must be removed from the system, and then the process is repeated. The die may not be fully functional because of a handling error which occurred in the manufacturing process. Other problems may arise during the burning-in of a bare die, in the handling of the bare die, in the manufacturing of the bare die or when the die is dissipating heat. Thus, there is a need to assure reliability in the package.
As will be shown, the present invention is an integrated circuit package that is very small. Furthermore, the package of the present invention offers a means of handling the package during the manufacturing process. Also the package of the present invention increases the reliability of the die.